Van Horn Randall, Clay Keith
Department of Biology, Indiana University, Bloomington, Indiana, 47405-6801.
Evolution. 1995 Apr;49(2):360-371. doi: 10.1111/j.1558-5646.1995.tb02248.x.
The purpose of this study was to determine how host identity and geographic proximity were related to genetic variation in the fungus Atkinsonella hypoxylon infecting four sympatric Danthonia grasses. We analyzed 192 A. hypoxylon isolates from 48 geographic sites for mitochondrial DNA (mtDNA) variation by restriction digestion of total DNA with EcoRI, BamHI, and PstI, and subsequent hybridization with purified A. hypoxylon mtDNA. Thirtynine haplotypes were identified. UPGMA cluster analysis showed that mtDNA type is highly correlated with host-species group; isolates from Danthonia compressa and D. spicata formed one branch of the phenogram, and isolates from D. epilis and D. sericea formed the other. Restriction maps of the most common mtDNA haplotypes infecting each host-species pair revealed a 30-kb size difference and a minimum of eight length changes and one restrictionsite change between them. Mapping of the mutation differences among all haplotypes occurring at North Carolina sites resulted in two distinct gene trees corresponding to the two Danthonia species groups, corroborating the phenetic analysis. The results indicate a high degree of host-dependent isolation and establish the existence of host races in A. hypoxylon. Possible mechanisms responsible for this isolation are discussed. Little differentiation existed between isolates from within a Danthonia species pair, and some variation was explained by geographic origin. Analysis of progeny from a natural sexual cross revealed that mitochondria are maternally inherited in A. hypoxylon.
本研究的目的是确定寄主身份和地理距离如何与感染四种同域分布的鸭茅属禾本科植物的真菌——低地阿特金森菌的遗传变异相关。我们通过用EcoRI、BamHI和PstI对总DNA进行限制性消化，随后与纯化的低地阿特金森菌线粒体DNA杂交，分析了来自48个地理位点的192个低地阿特金森菌分离株的线粒体DNA（mtDNA）变异。共鉴定出39种单倍型。UPGMA聚类分析表明，mtDNA类型与寄主物种组高度相关；来自扁穗鸭茅和穗序鸭茅的分离株形成了系统发育树状图的一个分支，而来自浅黄鸭茅和绢毛鸭茅的分离株形成了另一个分支。感染每对寄主物种的最常见mtDNA单倍型的限制性图谱显示，它们之间存在30 kb的大小差异，至少有8个长度变化和1个限制性位点变化。对北卡罗来纳州位点出现的所有单倍型之间的突变差异进行图谱分析，得到了与两个鸭茅属物种组相对应的两个不同的基因树，证实了聚类分析的结果。结果表明存在高度的寄主依赖隔离，并确定了低地阿特金森菌中寄主小种的存在。讨论了造成这种隔离的可能机制。鸭茅属物种对内的分离株之间几乎没有分化，一些变异可以用地理起源来解释。对一次自然有性杂交后代的分析表明，低地阿特金森菌的线粒体是母系遗传的。
